Visa sets merchant policy, and they do not allow high chargeback rates.
The merchant bears the brunt of the economic loss, but chargebacks are a relatively expensive hassle for the network too, and ultimately they will drop merchants who cannot keep chargebacks low.
Around 0.5% is considered reasonable. Anywhere in the 1% area for more than a few months will get a merchant dropped.
There are many other high risk industries they don't seem to have a problem with.